The generation of a reference voltage can be used in many applications. For instance, a reference voltage generator is typically a main component of a voltage regulator. Voltage regulators, for example, are often used in circuits for conversion of alternating current (ac) into direct current (dc) for providing a stable output voltage from an unregulated rectified input voltage. A reference voltage generator can also be used in dc-to-dc converters for providing a regulated output dc voltage from an unregulated input dc voltage. In addition, a reference voltage generator can also be used in analog-to-digital converters to provide regulated reference voltages for comparison with analog voltages that are to be digitized. For the purpose of the invention, the particular application of the reference voltage generator and method of the invention is not critical to the invention. Therefore, the invention can encompass any reference voltage generator and method used in any application where the need for a reference voltage is desired.
The design of a reference voltage generator is often governed by the need of achieving many desired characteristics or performances for such devices or circuits. For instance, it is desirable for a reference voltage to be substantially invariant with changes in the environment temperature. It is also desirable for a reference voltage to be substantially immune to noise and/or unwanted signals present at the unregulated power supply. Even yet, it is desirable for a reference voltage generator that can be easily manufactured without the need for achieving precise characteristics for at least some of its components.
In many instances, reference voltage generators are used in many applications where they are exposed to varying environment temperatures. It is a concern for designers to provide a reference voltage that is substantially independent of changes in the environment temperature. Typically, however, reference voltage generators comprise a plurality of components that have characteristics that vary with temperature. These temperature-varying characteristics of such components will typically affect the reference voltage produced by a reference voltage generator, unless the generator is properly temperature compensated. Accordingly, there is a need for an apparatus and method for temperature compensating a reference voltage generator in order to provide a reference output voltage that is substantially temperature independent.
Another concern for designers of reference voltage generators is the integrity of the output reference voltage. It is preferred that an output reference voltage be substantially free from noise and/or unwanted signals present in the power supply. However, often the power supply feeding a reference voltage generator includes noise, spurs, spikes, surges, and/or other unwanted signals. If a reference voltage generator is not properly designed, these unwanted noise and/or signals at the power supply will appear at the output reference voltage. Such a reference voltage generator would be characterized as having a poor power supply rejection ratio (PSRR). Accordingly, there is a need for an apparatus and method for better isolating the output reference voltage from noise and/or unwanted signals present in the unregulated power supply.
Yet another concern for designers of reference voltage generators is the processing or manufacturing of the voltage reference devices or circuits. Often these reference voltage generators are configured into integrated circuits using, for example, complimentary metal oxide semiconductor (CMOS) technology, which includes the deposition of different types of thin-films and ion implants. It is well known that semiconductor processing of integrated circuits is not a perfect art, and often imperfections occur in the manufacturing of integrated circuit components. For instance, it is often difficult to obtain an accurate particular value for an implanted well resistor used in an integrated circuit because of semiconductor processing imperfections. Accordingly, there is a need for a reference voltage generator and method that is not substantially dependent on the particular value of an integrated circuit component, such as the absolute value of a resistor.